Grippers used in industrial applications typically include a pneumatically or hydraulically controlled piston which is indirectly connected to gripper fingers. It is well known to construct such grippers so that when the piston is moved towards the gripper fingers, the gripper fingers open. To close the gripper fingers in such grippers, the piston must be moved in a direction away from the fingers. Examples of such grippers are shown in U.S. Pat. No. 4,185,866 which issued to Wittwer in 1980; U.S. Pat. No. 4,304,433 which issued to Langowski in 1981; U.S. Pat. No. 4,566,727 which issued to Yuda in 1986 and U.S. Pat. No. 4,234,223 which issued to O'Neil in 1980. The devices described in the Yuda and O'Neil patents have a drawback in that when the gripper fingers are in the closed position, with a loss of pressure, the fingers will not necessarily remain locked in the closed position. Furthermore, all four patents describe complicated gripper devices requiring many interconnected parts.
U.S. Pat. No. 3,945,676 which issued to Asamoto in 1976 discloses a gripper device in which the gripper fingers close as the piston moves towards the fingers and the fingers open when the piston moves away from the fingers. However, similar to the devices described in the Yuda and O'Neil patents, it appears that the gripper fingers do not lock in the closed position if the gripper experiences a loss of pressure.